During fabricating of a thin film transistor liquid crystal display (TFT-LCD), a chemical vapor deposition (CVD) is one of main processes for forming TFTs on a substrate to be coated, which is the so-called coating. Coating is a process for generating solid semiconductor with reaction gas by using a high frequency voltage in a high temperature and vacuum environment in a coating device, so that the solid semiconductor is deposited on the substrate to be coated and thus a film is deposited on the substrate.
As shown in FIG. 1, the coating process is performed in a coating chamber 1 of the coating device. Normally, a substrate 2 to be coated is placed on a stage 3 in the coating chamber 1, then reaction gas is filled into the coating chamber through a entrance 11 of the coating chamber and solid semiconductor is generated by the reaction gas in the coating chamber 1, the solid semiconductor is deposited on the substrate 2 to be coated so that a film is deposited on the substrate 2. The coating chamber 1 is further provided with a gas diffuser 8 therein, the gas diffuser 8 is mainly used to allow the reaction gas to diffuse uniformly in the coating chamber 1, so that the film deposited on the substrate 2 to be coated has a uniform thickness.
When the coating device performs coating, not only a film with a certain thickness is deposited on the substrate 2 to be coated but also a film with the same thickness will be deposited on the gas diffuser 8 and inner walls of the coating chamber 1. When the thickness of the film deposited on the gas diffuser 8 and inner walls of the coating chamber 1 is so large that the film on the gas diffuser 8 and inner walls of the coating chamber 1 may fall off due to the gravity and the pressure inside the coating chamber 1, the fallen film may generate a large quantities of particles, which may seriously affect the coating quality for the substrate 2 to be coated, therefore, the film deposited on the gas diffuser 8 and inner walls of the coating chamber 1 must be cleaned regularly. The deposited film is cleaned usually as follows: causing the gas of nitrogen trifluoride to react by an ion generating device to generate fluoride ions; filling the fluorine ions into the coating chamber 1 so that they react with the deposited film to generate gas such as fluorine gas, nitrogen gas and the like, and then discharging the gas through a pipe.
The cleaning for the coating chamber of the coating device may be performed in a certain cleaning period, the cleaning period is set according to the limit thickness of the film deposited on the inner walls of the coating chamber without falling off, that is to say, cleaning is not performed until the thickness of the film deposited on the inner walls of the coating chamber approximates to the limit thickness without falling off. Currently, the cleaning period is set as follows: first, according to the limit thickness without falling off and the thickness of a film to be deposited on each substrate to be coated, calculating the number of the substrates to be coated, wherein a sum of the thicknesses of the films to be deposited on the substrates approximates to the limit thickness without falling off, and then a total time required to coat these substrates is set as the cleaning period of the coating device. Regarding the set of the cleaning period, first, according to the thickness of a film to be coated on each of the substrates, artificially calculating the number of the substrates to be coated, on which films with a same thickness or different thicknesses are coated respectively, wherein a total thickness of the films coated on these substrates approximates to the limit thickness without falling off, and then artificially and manually setting the total number of the substrates to be coated, so that the cleaning period is set.
However, with the improvement and development of the coating process, and during the coating process of semiconductor, different substrates to be coated usually correspond to films with different thicknesses to be deposited, so the cleaning period needs to be adjusted to adapt to different products, but it is trouble to adjust the cleaning period manually. Furthermore, in a case of various types of substrates to be coated being coated, it is likely to occur that the type of the product and a preset cleaning period do not match with each other, which may cause the following undesirable results: one is that the cleaning period is short, which results in that the deposited film is cleaned up when the thickness of the film deposited on the inner walls of the coating chamber is much less than the limit thickness without falling off, thus greatly wasting the cleaning gas; another one is that the cleaning period is long, which results in that the thickness of the film deposited on the inner walls of the coating chamber is much larger than the limit thickness without falling off, that is, the cleaning for deposited film is performed after the film deposited on the inner walls of the coating chamber has begun to fall off, resulting in that there are so much particles in the coating chamber during coating, which makes the coated substrate have so much particles thereon, which directly affects the product yield.